Kenji Wada

Balanced polarization maintaining fiber Sagnac interferometer vibration sensor

To achieve a nearly zero-delay operating point in a polarization-maintaining (PM) fiber Sagnac interferometer, two identical PM fibers were incorporated so that their two main axes were orthogonally coupled to each other. A simple fiber vibration sensor system was constructed with a light emitting diode and a balanced PM fiber Sagnac interferometer, in which one of the PM fibers was used as a sensing cable and the other as a reference cable. The vibration sensor was confirmed to be temperature-compensated and generated a phase shift per unit length and unit strain of the sensor of 4.7 milliradian/(m·με) when mechanical vibrations with 1 kHz sinusoidal and triangular waves were stably observed under an input power of 10 μW.

Pulse-shaping of gain-switched pulse from multimode laser diode using fiber Sagnac interferometer

We propose a pulse-tail elimination and pulse shortening method using an optical interferometer, which is effective for picosecond chirped pulses from gain-switched multimode laser diodes. In a numerical simulation, when the delay distance between a chirped pulse and its replica in an optical interferometer matches two times the round-trip optical length of the laser cavity, the pulse-front and -rear tail parts are effectively eliminated from the input chirped pulse after passing through the optical interferometer. Using this method with a fiber Sagnac interferometer, a 33 ps pulse with a long-tail emitted from a gain-switched 1540 nm multimode laser diode was linearly transformed into a 20 ps pulse with a substantially reduced tail.

Intramolecular excitation energy transfer in diarylurea-linked zinc porphyrin–anthracene dyads

Structurally controlled zinc porphyrin-anthracene dyads, syn-arranged 1 and anti-arranged 2, were newly synthesized employing a diarylurea linkage, and the excitation energy transfer (EET) from the anthracene to the zinc porphyrin chromophore was investigated by steady-state fluorescence emission spectroscopy as well as fluorescence lifetime measurement, especially focusing on the effect of the chromophoric orientation on the EET. In both of the dyads, intramolecular EET was facilitated upon excitation of the anthracene chromophore (lamda(ex)= 401 nm), and the zinc porphyrin S1-S0 emission (580-720 nm) was enhanced. The EET in the syn-arranged dyad 1 was more efficient than in the anti-arranged 2: the S1-S0 emission in 1 was 1.8 times larger than that in the zinc porphyrin reference compound 3, whereas that in 2 was enhanced by 1.6 times, compared to that in 3. In the fluorescence lifetime measurement, the quiet short-lived component assignable to the EET was observed for the dyads 1 and 2 beyond the analysis limit (<25 ps). The EET rate constants in the dyads 1 and 2 were estimated as not less than 4.0 x 10(10) s-1. However, in the case of 2, the residual long-lived component assigned to the anthracene emission was also observed at 425 nm. These results showed that the syn-arrangement of the zinc porphyrin and anthracene chromophores was more preferred for intramolecular EET to the anti-arrangement.

Spin Relaxation of Electrons in Strained-GaAs-Layer Photocathode of Polarized Electron Source

The luminescence polarization method using a mode-locked Ti:sapphire laser and a streak camera is applied to the measurement of the spin relaxation time and the lifetime of electrons in the strained-GaAs-layer photocathode of a polarized electron source. The spin relaxation time and the electron lifetime are 105 ps and 45 ps at room temperature, respectively. Electron-hole scattering is thought to be the main mechanism of the spin relaxation of our strained-GaAs photocathode.

Spin-Dependent Luminescence of Highly Polarized Electrons Generated by Two-Photon Absorption in Semiconductors.

The first demonstration of the generation of highly spin-polarized electrons in semiconductors using two-photon excitation was performed by measuring the spin-dependent luminescence. Bulk p-GaAs samples were excited by circularly polarized light with wavelength of 1.5 µm from an optical parametric oscillator and the luminescence polarization spectrum was measured. The experimental results showed that the highly spin-polarized electrons were generated by the circularly polarized two-photon excitation of the bulk p-GaAs. The initial spin polarization of conduction band electrons was estimated to be 95% from the spin relaxation time and the lifetime obtained by the time-resolved luminescence measurement.

Optically assisted ultrasonic velocity-change images of visceral fat in a living animal

Noninvasive imaging method by detection of ultrasonic velocity change was proposed for diagnosis of visceral fat. The ultrasonic velocity-change images of the fat distribution in the excised rabbit lever and living rabbit lever. Experimental results suggest that this imaging method can be applied to a practical monitor of the visceral fat in a living human body.

P3D-5 Real Time Optical Tomography of Biological Tissue by Detection of Ultrasonic Velocity Change Due to Light Illumination

The ultrasonic velocity change induced by light was measured quickly by the remodeled commercial-type ultrasonic equipment with the multi-array transducer in order to investigate a practical optical tomography for medical diagnosis. The 3D view of the optical absorption region in the tissue mimic phantom was obtained by ultrasonic velocity change imaging

High Spin Polarization of Conduction Band Electrons in GaAs-GaAsP Strained Layer Superlattice Fabricated as a Spin-Polarized Electron Source

We measured a spin-dependent luminescence from a GaAs–GaAsP strained layer superlattice and GaAs substrate to evaluate the spin polarization of conduction band electrons excited by circularly polarized light. The GaAs–GaAsP strained layer superlattice with a mixture of group-V elements, As and P, was considered as a suitable spin-polarized electron source because the discrepancy of the valence band was reported to be larger than that of the conduction band. The observed maximum circular polarizations of the luminescence from the GaAs–GaAsP strained layer superlattice and GaAs substrate were 68% and 15%, respectively. The dependence of the circular polarization of the luminescence on the excitation photon energy was well explained by the calculated band structure. The initial spin polarizations of conduction band electrons excited in the GaAs–GaAsP strained layer superlattice and GaAs substrate were estimated to be 95% and 46%, respectively, from the luminescence polarization, lifetime and spin relaxation time. The high initial spin polarization of conduction band electrons proved the high performance of a photocathode with the GaAs–GaAsP strained layer superlattice as the spin-polarized electron source.

Simple form of multimode laser diode rate equations incorporating the band filling effect

To derive a simple form of the multimode laser diode rate equations incorporating the band filling effect, the laser diode gain in the direct bandgap model is introduced into the conventional multimode laser diode rate equations. By numerically examining each modal gain under the gain-switching condition, it is found that both the differential gain coefficient and the carrier density at transparency show an approximately linear dependency on the oscillation frequency. As a result, it is possible to derive a simple form of the multimode laser diode rate equations with linearized gain, which can be used to simulate the behaviors of a gain-switched laser diode characterized by the band filling effect, in both the multimode and single-mode oscillation cases.

P5B-11 Monitoring Device of Au Nano-Particle Distribution in Living Body Using Ultrasonic Velocity Change Image

We could obtain ultrasonic velocity change images of Au nano-particles in the two phantoms which ware made of highly optical scattering ager and the chicken breast meet by using the remodeled diagnostic ultrasound equipment. All experimental results suggested that our imaging method could be applied to a practical monitor for the thermal therapy and the drug delivery system (DDS), and could be applied to biomaterial identification.